The broad objective of my research has been to elucidate the neural and hormonal factors involved in the normal contractile and secretory functions of the lactating mammary gland. My efforts over the next several years will be: 1. To analyze the relative roles of the mammary gland, kidney and liver in the metabolic clearance of immunoreactive prolactin from the plasma of rats during late pregnancy and during lactation. Metabolic clearance rate will be assessed by the constant infusion to steady state method. 2. To determine the rate and extent of transfer of immunoreactive prolactin (through the milk) from mother to offspring throughout lactation. 3. To determine the doses of intravenously injected rat prolactin required to stimulate minimal, i.e., threshold, as well as maximal milk secretion in the freely moving conscious rat at various stages of lactation; also, to determine the roles of STH and ACTH in modifying these milk secretory responses. 4. To correlate minimal and maximal milk secretory responses with circulating prolactin concentrations during various stages of lactation. 5. To analyze the role of peripheral mechanisms in inhibiting the milk stimulatory effects of prolactin and to determine to what extent they contribute to decline of mammary secretion. 6. To investigate with sensitive intramammary pressure techniques whether estrogen and progesterone exert either facilitatory and/or inhibitory influences at the mammary gland level upon the contractile response of the mammary gland myoepithelium. 7. To analyze the role of the cerebral cortex and the sympathetic nervous system in the regulation of mammary contraction.